Radio beacon and panoramic reception system



Feb. 23, 1943.v M. WALLACE RADIO BEACONAND PANORAMIC RECETION SYSTEM Filed April 20, 1940 11 Sheets-Shea?I 1 :El :Ful A INVENTOR. @11a/cef Qyf/afaca M. WALLACE Feb. 23, 1943.

l RADIO BEACON AND PANORAMIG RECEPTION SYSTEM l1 Sheets-Sheet 2 Filed April 20, 1940 Feb. 23, 1943.

M. WALLACE' RADIO BEACON AND PANORAMIC RECEPTION SYSTEM Filed April 20, 1940 l1 Shees-Sheel'. 4

Feb. 23, 1943. M. WALLACE RADIO BEACON AND PANORAMIC RECEPTION SYSTEM 11 Sheets-Sheet 6 Filed April- 20, 1940 I5 za TRM/:M1 free ras/rse ETE-... E

Feb. 23, 1943. M. WALLACE RADIO BEACON AND P ANORAMIC RECEPTION SYSTEM Filed April 20, 1940 1l Sheets-Sheet 7 Affare: e

Feb. 23, 1943. M. WALLACE' 2,312,203

RADIO BEACON AND PANORAMIG RECEPTION SYSTEM IN V EN TOR.

Feb. 23, 1943. M, v /mm; 2,312,203

RADIO BEACON AND PANORAMIG RECEPTION SYSTEM Filed April 20, 1940 ll Sheets-Sheet 9 IN V EN TOR.

QTa/zclef. Waff/fac@ Feb. 23, 1943. M. WALLACE RADIO BEACON AND PANORAMIC RECEPTION SYSTEM Filed April 20, 1940 IN VEN TOR.

lz'aznej l1 Sheets-Sheet 10 JMU Feb. 23, 1943. M, WA| A.`.; 2,312,203

RADIO BEACON AND PANORAMIC RECEPTION SYSTEM Filed April 20, 1940 ll Sheets-Sheet 11 l "r Q IN V EN TOR.

Y :FT-H F E E l- Patente-d Feb. 23, 1943 NETE FFME

RADIO BEACN AND PANORAMIC RECEPTION SYSTEM v Marcel Wallace, New York, N. Y., assigner, by mesne assignments, to Panoramic Laboratories, Inc., New York, N. Y., a corporation of New York Application April 20, 1940, Serial No. 330,763

(Cl. 25o-11) My invention relates broadly to systems of,

radio navigation and more particularly to improved methods and circuit arrangements for y radio beacons and panoramic reception systems for use in navigation of mobile bodies.

In,vv my copending patent applications, Serial Numbers 196,520, for Panoramic radio receiving system, led March 17, 1938, Patent No. 2,279,151, granted April 7, 1942, and 204,470, for Radio navigation system, led April 26, 1938, Patent No. 2,273,914, granted Feb. 24, 1942, I have shown that by means of a panoramic receiver installed on board of a plane, it is possible to observe one or a plurality of signals which areradiated from transmitting stations located at dangerpoints, such as mountain peaks, for warning the pilot of the approach of the plane to terrain which may be hazardous to aerial navigation.

One of the objects of the present invention is l to provide -a system for equipping a body, whether fixed or mobile, with a signal generator which emits a characteristic signal of a warning nature for indicating hazards to navigation. l,

Another object of my invention is to provide a system for emitting a signal of such a nature as to informrthose who receive it, of the altitude A further object 'of my invention is to provide an arrangement of a signal generator that can be synchronized with a receiver on board of a mobile body, in such a manner that the signal supplied by the generator does not interfere with the reception of another signal on the same frequency originating from another mobile body.

Another object of my invention is to provide means for creating a signal which gives directional infomation such as the direction of motion of a mobile body, or the direction of the wind at the location of a fixed body for navigational or landing purposes.

A further object of my invention is to provide a remote system for giving an additional set of information by means of transmitted signalling the 'operator immediately upon receipt of any such signal. f

A further object of my invention is to provide simple transmitting and receiving apparatus for energy such as local pressure at a given location.l Still another object of my invention is to provide a system for imparting the knowledge of the wind velocityiat a predetermined location by means of transmitted signalling energy.

Another object of my invention is to provide simple apparatus for the reception and convenient interpretation of signal indications, and information which can be received visually or both visually'and aurally,` so as to give a warning to 55 dual-frequency providing navigational infomation without moving parts and with all the circuits electronically controlled.

Still another object of my invention is to provide complementary receiving apparatus capable i of giving navigational indications received from such transmitters also fully electronically controlled. l

A further object of my invention is to provide an electronicaly controlled transmitter capable of changing both its frequency and directivity, at such a rate as to make the signals appear on a panoramic receiver as if simultaneously transmltted, thereby permitting the useof one-half the effective power required .by transmitters operating continuously-and reducing the problems due to interference between two transmitters.

A still further object of my invention is to provide special dual-frequency beacons which give a directly interpretable indication of direction of on course" or right, or` left, by producing on the screen of a panoramic receiver signals which are either symmetric or asymmetric, higher to the right or left, and corresponding to the side on which the observer is located with respect to the beacon. l y' Another object o f my invention is to provide a Asystem for efficiently utilizing the available frequency spectrum by distributing beacons along an airline, the average frequency of which varies proportionally to their distance from a another system although such beacons may use the same portion of the frequency spectrum, by changing the rate of frequency change from one system to the other. This is rendered possible -by the use of panoramic receivers, having means A for varying at will their rate of frequency sweep,

so as to make itcorrespond to the rate' of frequency variation, Ior of a harmonic thereof, -of a beacon. This feature permits the elimination of sources of periodic noises such as produced by vibrators, motors, etc.

Still another object of my invention is to provide a receiver which can simultaneously indicate the presence of any obstacles above or below the observer, and also how far above or below these obstacles the observer is situated, and to control a warning local transmitter and at the same time indicate a plurality of dual beacons. Such a receiver uses one common indicator which can give all these indications simultaneously.

Another object of my invention is to provide a duel-directional panoramic receiver which can instantaneously indicate the direction of each of a plurality of transmitting stations, independently of their transmission pattern characteristics. I describe herein such receivers in which there are no moving parts, all functions being carried out electronically. y

A still further object of my invention is to provide a simple transmitting apparatus which can automatically givean aircraft pilot all the indications required in case the pilot wishes to make a blind landing, such installations being practicable for installation and maintenance in emergency landing fields where no attendants are present.

Other and further objects of my invention will be apparent from the specification hereinafter following by reference to the accompanying drawings, in which:

Figure l is the diagram of an altimeter conlA is ablock diagram showing the interconnections between an altimeter, a transmitter and a receiver according to my invention; Fig. 2 is another block diagram showing in a more detailed 'trolled transmitter embodying my invention; Fig. y

form the principal parts and their relationship in a fully electronically controlled panoramic receiver, and of an altimeter controlled transmitter, saidy receiver tuning off the transmitter automatically so as to prevent interference between the two; Fig. 3 represents a series of ,curves showing the action of various elements shown in Fig.

2; Fig. 4 is a detailed diagram of a receiver such Y' as shown in Fig. 2; Fig. 5 is a block diagram of another electronically controlled receiver and transmitter similar in function to those shown in Fig. 2, but covering two distinct portions of the frequency spectrum; Fig. 6 shows details of the special elements used in connection with the apparatus shown in Fig. 5; Fig. '7 shows a series of curves explaining the action of various elements of Fig. 5; Fig. 8, a special dynamically balanced condenser combined-with asynchronous commutator for obtaining mechanically` whatever Amay be obtained electronically; Fig. l9` isa vdlag'ram of an apparatus vin which the device ofFlg. 8 Vis used; Fig. 10 shows a commutator and its l connections for obtaining a square wave current;

Fig. 11 shows how the devices of Figs.. 8 and 10 are used in a two-band mechanically controlled panoramic receiver; Fig. 12 is a diagram explaining the action of the various parts of Fig. 11; Fig. 13 shows acombination' between an electronic source of .sweep voltage and a mechanical commutator and variable condenser and the method of synchronizing these elements: Fig. 14 shows in block form the principles used in a dual-frequency beacon according' toy my invention; Fig. 15 shows how-a plurality of alternately keyed Iduale-frequency beacon signals appear on the screen of apanoramc receiver on the type of calibration used on such receiver to determine the ratio between two signals; Fig 16 is a diagram of a mechanically controlled alternately keyed dual-frequency beacon; Fig. 17 is a block diagram of an electronically controlled dual-frequency beacon.,

in which a master oscillator gives alternately two diiferent frequencies; Fig. 18 is a diagram of the range beacons; Fig. 21 shows the appearance of the screen and dialarrangement ofa dual band panoramic receiver, showing simultaneously a plurality of beacons. their geographic position and also a plurality of obstacles and their respective altitudes with respect to the observer; Fig. 22 is a reversible transmission pattern of a dual-frequency beacon creating an equi-signal path; Figs. 22aand 22h show how certain signals transmitted from a transmission pattern such as shown in Fig. 22 appears on a panoramic receiver; Fig. 23 is a diagram of a wind controlled directive beacon; Fig. 24 shows how a plurality of ships having dual-frequency beacons can keep going in a definite formation; Fig. 25 shows in block diagram form a dual-directional panoramic receiver electronically controlled; Fig. 26 shows the indicating screen of such a receiver and how various signals are visually reproduced; Fig. 27 is a diagram of a receiver represented in Fig. 25; Fig. 28 is a modifled form of a part of a receiver of the type represented in Fig. 25; Fig. 29 shows a further modilied and improved form of circuit embodying my invention; and Fig. 30 represents the transmission patterns of a dual frequency glide path indicating beacon.

ln the carrying out of my invention, advantage is taken of the properties of a panoramic receiver. such as described in my copending applications, supra.

In the system of my invention, I provide means capable of:

1. Continuously observing the variations of field strength of two or more signals.

2. Observing the variations of frequency of "two or more signals.

3. Determining the frequency of modulation of any signal, by synchronizing the receiver rate of frequency sweep with the modulation of the transmitter.

A signal is generated from the fixed or mobile altitude of H feet a frequency Fm, is allotted.l

any intermediary altitude, for example h, can conveniently correspond to a frequency InsteadV of this simple linear frequency versus altitude'dlstribution, other functions can be determined, which insteadof being linear, can be,

for example, exponential, the frequency varying proportionally to the percentage of altitude variation, etc. An element such as an altitude or pressure indicating instrument is employed for controlling the frequency determining circuit of the signal generator.

For example, as shown in Fig. 1, 'an aneroid barometer i is made to vary the distance between plates 2 and 3, electrically insulated from each other 'by means of insulator d. The capacity of the resulting condenser 2-3 varies according to the local pressure as impressed upon the barometer. 'I'his condenser operates to tune an inductance 5 and the whole tuned circuit .determines the frequency of oscillation of a tube 5. This is a Vsirnplegtype of local pressure or altitude indieating oscillator, which forms the basis of other arrangements of my invention described hereinafter.

Such oscillators can be mounted on the various landing elds in diierent 'geographical locations, so as to inform the incoming pilots as to the actual local pressure and to permit the correction of their pressure-controlled altimeters. In order to effect this correction, the pilot must know what the actual altitude of that field is, which information can be obtained from proper charts. The pilots can read in these charts what would be the normal pressure and from the reading obtained from the frequency of the oscillator, the positive or negative correction of the altimeter is indicated. y

The readings of the indications given by such oscillations, are best made with a panoramic receiver, suchas described in my copending applications, supra. tube which is the visual indicating means used in such receivers, can be calibrated in frequency or, preferably, in altitude, and from the position where such a signal appears on the screen, the altitude or local pressure is indicated.

If the signal generator is mounted lon board of an airplane also equipped with a panoramic receiver which tunes in the altitude band of the frequency spectrum, the locally generated signal covers that part of the screen which corresponds to its own altitude. If another airplane is in the proximity of the iirst, and at the same altitude, the observer will not be able, therefore, to distinguish its signal, on account of said local signal.

In order to-avoid this, I provide a combination between the local signal generator and the receiver, in such a manner that the latter controls the first. By means of a synchronous switch, which can be either mechanical or electronic, the transmitter is shut-olf entirely, or only reduced in power, periodically, every time the receiver tunes through or must indicate a frequency close to that of the local transmitter.

An electronically controlled combination of transmitter and receiver is shown in Fig. 2 in the form of a; block diagram for explaining my invention. The panoramic receiver illustrated consists of a'signal input circuit A, an oscillator B, a mixer C and two channels of intermediate frequencyv amplifiers D and E. The oscillator is periodically tuned over a band of frequency by a frequency modulating tube F which, in turn, is controlled by a sweep voltage generator G. This generator and develops at its peak a much weaker signal than channel D. However, over certain portions of the frequency spectrum, immediately adjacent to the band pass characteristics of the channel D, it develops a stronger signal.

(ef This is illustrated in Fig. 3, in which the ab-` scissa represents the frequency variation (or time variation, the two being linked together) and the ordinate represents gain of channels D and' E or power-developed by oscillator transmitter J.

supposing that the oscillator transmitter J emits a signal on frequency Fs, and the panoramic receiver starts tuning from afrequency Fmm. towards a frequency Fam. .as it approaches irequency Fh, it passes through a region Fl-Fz when the I. F. channel E develops an impulse which is applied atonce to a keying tube which triggers off the ltransmitter J, (see curve J on Fig. 3), before or almost at the time when the channel D could start building up a signal from the transmitter. The time constants of the trig- 'Ihe screen of the cathode ray i ger circuit are such as to maintain the transmitter turned off during a predetermined time interval, equivalent to a variation of frequency of Fe- Fz, and when, the oscillator starts again, its frequency is out `of the tuning range of the receiver,

q so that the latter is unaffected by the presence ci that local signal. The'signals picked up by the channel D are detected, ampliiied and applied to the other set of deecting plates of the cathode ray tube H. These signals will be always synchronized with the sweep applied to the iirst set of deflecting plates, so that each deflection will appear stationary, in a position determined by the frequency of the signal and of an amplitude determined by the signal strength. ,I

In parallel with the cathode ray tube, it is possible to feed an audible device such as a loudspeaker o-r head-phones. This is important in case of collision warnings. The speed of the planes being great, it is possible that the pilot may not be aware of the appearance of a visual danger. signal on the screen, but his attention Vwould be drawn at once if this signal will produce a distinctive noise in the loud-speaker, which is exactly what happens. This is a very important feature of my invention, which adds to the safety of the ier.

Automatic volume control can be incorporated in the panoramic receiver, as it will be described hereinafter. The eiect. of this control upon the signals is that it will prevent a. signal from building up in amplitude beyond a given point but, instead, it will compress the other signals weaker than it, so as to maintain their amplitudes -an indication of their field strength.

In the circuit diagram of Figfll, the input circuit A is constituted by a receiving antenna 8, an inductance tuned by condenser 9 and an ampliiler tube I2. The frequency modulated oscillator B is constituted by the triode I4 and a circuit tuned by condenser Il. Directly connected to the tuned' circuit of this oscillator, I show theA frequency modulating channel F constituted by a thermionic tube l5 which acts as a reactance in parallel with said tuned circuit. By properly adproduces the source of sweepvoltage applied to tuned slightly off the frequency of channel D '(5 justing' phase relationship between the input and output circuits of tube H5, as determined by ca'- pacities, resistors and choke (40, M, 42), the reactance of this tube'will increase or decrease the vfrequency of the oscillator I4 by. an amount depending on the voltage impressedon the grid i3 of the tube I5 and in a direction dependingon its polarity.

An alternating voltage, preferably produced by a. saw-tooth oscillator I6 and ampliiied by tube I1 (corresponding to G in the block diagram) is fed to the variable reactance tube I5, through a potentiometer 26 and a voltage balancing potentiometer which is shunted by a battery 1I.

Ihe adjustment of potentiometer 1I) controls the biasing voltage on the grid 43, consequently the react-.ance value of the tube I5 at the average sawtooth voltage and determines, therefore, the average frequency at which the receiver will operate, and potentiometer 26 controls the amplitude of the voltage applied to grid 43 which in turn controls the amount of frequency sweep of tube I5. The frequency of the sweep voltage generator can be adjusted by means of a multi-position selectorswitch 28 and the plate voltage controlling rheostat 81.

The converter corresponding to C is tube I3 whose grid 4d is coupled to the input amplifier tube I2 and frequency modulated oscillator I4. The converted signal is developed in the I. F. transformer 45 having two secondaries shown at 36 and 31. The secondary 36 is tuned to the same frequency as the primary of transformer 45 and feeds the high gain, sharply tuned channel corresponding to D, composed of two amplifying stages comprising the tubes I8 and I9 and transformers 46 and 41.

The signals are then detected and reamplified by means of a combined diode-triode thermlonic tube 20. One diode plate 48 applies the rectified signal to a load 54 and the voltage drop through it is used to automatically control the gain of the amplifying -tubes I8 and I9 by applying appropriate voltages at their grids through resistors 56 and 5I, which are by-pasrsed with condensers 53 and 52. The action of this automatic volume control is very important in the operation of the system of my invention.

'Ihe otherrdiode 49 is connected to the diode 48 by means of a condenser 55 and develops a rectified pulsating current which is applied to an amplitude controlling potentiometer 30 and from there through a condenser 56 tothe grid of the triode section of the tube, which acts as a low frequency amplifier of the pulsating current.

A potentiometer 3I is provided for the important function of thresholding the signals. 'I'his operates as follows: The anode 49 of the diodetriode tube 20 is returned to the powersupply circuit by means of resistors 12 and 13 t0 this potentiometer 3| a leg of which is at ground potential. The anode potential is taken from the cathode ray elements power supply 14 which is dropped to ground potential through a series of resistors including 15; 16, 11 and 18, some of which act as focus and intensity controls for said cathode ray tube.

By being able to make the anode 49 of any potential desired from zero up to a few hundred volts negative, it is possible to cutout or prevent detection ofvany signal which does not exceed a desired value. This control acts, consequently, as an adjustable threshold device, which is useful for eliminating either noises (which are below the signal levels) or weak signals which. are not interesting to the observer and which may confuse him. This threshold potentiometer can be calibrated in field strength, whether micro-volts or decibels for measuring the field strength of any signal. It is therefore useful also for measuring the difference of deflection amplitude between the deflection amplitudes of two signals.

The potentiometer 30 which controls the amplitude of the signals applied to the output device, will cut all signals in such a manner as to reduce them all in the same proportion. Therefore, the signal ratios remain constant. By using, however, the threshold control we change the ratio between the signal amplitudes and this becomes useful when we'want to exaggerate or emphasize the difference of two signals nearly equal in amplitude, as is'necessary in the dualfrequency beacons described hereinafter.

The pulses resulting from the reception of a series of stations are of extremely short duration, this depending upon theA frequency of the sweepvoltage and the total frequency band covered and the selectivity of the I. F. stages. This means that the amplifier must have certain frequency characteristics which permit the amplification of sufficiently high frequencies, of the order of a few thousand cycles per second. These frequency characteristics are determined by the values of the grid, plate and cathode resistors 51, 58, 69. A resistor 59 connected to the high voltage source maintains the exact 'bias required under conditions of varying load. The amplified pulses are applied through a condenser 6l to one deflecting plate 62 of the cathode ray tube 23, but it can also be connected by means of -switch 35 to an auditive output device 34 for audible warning. The perpendicular deflecting plate 63 of the cathode ray tube is connected to the 4sweep voltage generator I6 after amplifying its output through tube I1. The frequency of this sweep is sufficiently high to produce a rapid sweep of the cathode ray beam, which appears substantially flickerless on the fluorescent screen of the cathode ray tube.

The secondary 31 of I. F. transformer 45 f`eeds .the transformer 64 which is connected to a diode detector and amplifier tube 2I which corresponds to the amplifying' channel E of Fig. 2. A very strong signal produces across the condenser 65 and resistor 66 a substantial negative voltage which is applied to the grid of a keying or trigger tube 22, (corresponding tov I). The plate of this tube is connected to the cathode of thfgtransmitter oscillator tube 6 whose frequency is con-y trolled, as explained hereinbefore, by the varia-f' tions of pressure as impressed'upon barometer I.

The tube 22 offers the properA amount of resistance in the cathode ofthe oscillator/6 when no signal is applied to the grid 58, which is returned to ground by the grid resistor 61.

A signal however builds up on the condenser 69 and grid 68 a negative voltage which triggers off the plate current of tube 6 which stays shut off until the charge of condenser 69 leaks out throughzresistors 66-61.

The time constants of this circuit can be adjusted to keep the transmitter turned off just the length of time desired, as explained hereinafter.

The voltage developed by the tube 2| is very i.

low even when signals of a few thousand microvolts are present, as may be received from powerful nearby stations, but is great in the presence of the local signal which builds up to several hundred thousand micro-volts in that stage, before the sharply tuned stages i8, I9, have time to build a substantial signal. A variable coupling between the primary and secondary of transformer 64 permits the proper adjustment of the cut-off of the local transmitter. The tuning of this primary and secondary is such asto make ttact as a filter of broad band pass characters cs.

All the potentials' required for the panoramic receiver are produced by a common source of power supply and all can have a common ground return to the chassis. l

The panoramic receiver described herein can be made to cover a rather substantial band by ganging the condensers 9, I0, Il. The electronic sweep will produce a panoramic reception effect on the screen of the oscillograph 23, of a band of frequencies whose width can be adjusted by the potentiometer 26. If the constants of the circuit of tube I are properly adjusted. it is possib': to make the frequency shift of the oscillator Il equal both above and below its natural frequency, which permits a panoramic observation oi' the band immediately above or below a given "center frequencyl If the total band which must be covered is not too great, the input stages l2, I3, may be made. of sufllciently broad band pass characteristics to avoid the necessity of tuning the condensers 9 and l0 and still obtain substantial linearity of response over the desired band.

In this case, we can vary the center frequency of the panoramic receiver either by adjusting the oscillator condenser Il or by adjusting the center arm of`biasing potentiometer 10. This'varia-tion vcan take place either manually or automatically and in the latter case it can be eiected by. either the same barometer I, which controls the transmitter' oscillator, by mechanically linking-it to condenser il, (or potentiometer 10) :or by another similarly constructed barometer (or altimeter): have shown a dotted line between Il and 'l -to show a mechanical link. 1

This control of the condenser Il by an altim-l eter, will.v permit a constant retuning of the center frequency of the panoramic receiver, this center being at all times at the frequency corresponding-to its altitude, and the frequency produced by the local oscillator-transmitter J. The frequencies above andbelow it represent altitudes above and below it and the band covered can be such as to cover an altitude of, for example, 2500 feet above and 2500 below the airplane. ment covers a relatively wide band,`so as to take care of very great altitudes. The vceiling of modern planes increases continuously and if we would have to cover on' a few inches of an oscillo-l graphscreen all the band, the readings may be dilficult to'make or would not have sumcient qurcy- With'this method, however, of centering the .observation and limiting it to a certain height above and below, this objection is removed and, besides,V the pilot has all the warning and Vinformation he wishes, as he is not interested in `what happens too high up or too far below him.

This",` centering of the local altitude, corresponding `to the frequency of the locally generated signal greatly simplifies the design of the commutator controlling this signal.` VThis commutator can be either mechanical or electronic, acting every time when the receiver tunes throughlthe center region of its band. i

Such a continuous adjustment of condenser Il would not be required for a receiver used on the control tower of an airdrome which would wish to observe the whole altitude band at any time, but in these cases a very large diameter oscillograph mayb/e used, and a mechanically controlled panoramic receiver provided which InFig.4,I.

This is useful if the frequency assign- :these tw'o types lof impulses.

can be made to cover conveniently very wide frequency bands. f

In my copending applications, supra, I have shown how I can simultaneously receive on a panoramic receiver two bands of frequency which can be observed on two diierent portions of the oscillograph tube. This is a very important requirement if the receiver is to be used for navigational purposes, so as to avoid carrying on board several receivers. It may be assumed, for example, that the flier wishes to follow a string of radio range beacons of any dangerous obstacle, ilxed or mobile. The beacons may operate on one band of frequenciesand the collision signals on `another band. An'electronically controlled receiver I showing simultaneously two bands of frequencies can be used advantageously for the purpose. 'I'he principle of its operation, as distinguished from the first is the following: synchronously with the saw-tooth generator,y I provide means for generating a square-wave"l alternating current. This is composed of a series of electrical impulses of a constant amplitude of half the frequency of the saw-tooth wave each having a duration equal to the duration of each "saw-tooth impulse. These impulses are intermittent, each being followed by an equal time period when no current is generated. Fig. 7 shows on its lower part as M three cycles of such square-wave pulsating current impulses; N` represents six cycles of the sawtooth synchronous alternating current impulses and M-i-N represents an alternating current resulting from the combination or addition of The frequency controlling tube l 5 (Fin the block diagram, Fig. 5), in which I provide a circuit for feeding a current such as the one represented as M-l-N will alternately cover two bands of frequency whose separation from each other will be determined by the amplitude of the square wave input.

0n the right side of Fig. 7, I show an ordinate representing frequency variation as produced by such a combinationwave in the variable frequency oscillator. It alternately covers the fre-.- quencies F1, F2 and F3, F4. 'I'he frequency separation between Fa and Fa can be reduced to zero by reducing the amplitude of the square wave voltage or be increased to a maximum. by increasing-that voltage. It canftherefore, be seen that variations of amplitude vof M will shift only one band of frequencies `(F3 to F4) and will not anect the other band. This lshift can be obtained by applying the square `Wave to a biasing potentiometer such as Ill (Fig. 4).

Fig. 5 represents another block diagram showing how this receiver operates. Thesame letters are used as in Fig. 2 for the common elements of the two types of receiver-transmitter combinations. In Fig. 5 in addition S represents the square-wave generator, and T the mixer of the saw-tooth .and square-'wave currents. Previously to being mixed, the saw-tooth component is applied to one of the deecting plates`63 of the cathode ray tube and the square-wave component to another deflecting plate 62,.normal to the rst, whereit is combined with the signal from the channel D.

The` effect of this application of the squarewave is to recurrently, and at the end of each cycle of the saw-tooth wave, shift thel reference zero line of the cathode ray tube, so as to alternately obtain two parallel lines on which the spectively, Fatov F4 are appearing.

The linear separation between these parallel lines is a function of the amplitude of the squarewave voltage applied to the deiiecting plate, and this is controlled through any appropriate means. The mixing can be obtained, for example, directly in the frequency modulating element, by applying saw-tooth voltage as shown in Fig. 4 and the square-wave voltage to biasing potentiometer 10.

Fig. 6 shows a detailed diagram of the elements G, S and T of Fig. Tube 80 is a double triode, the grids of which are cross-connected in such a way that each triode section becomes alternately blocked. The frequency of this blocking action is determined by the rate of charge and discharge of condenser pairs 84, 85, 86 (groups a and b) a pair of which are selected by switch arms 88a and 88h, and also by the value of the dual rheostats 81a and 81h.

Another tube 8l acts as a saw-tooth oscillator and the frequency controlling elements, that is, condensers 84e, 85e, 88e and rheostat 81e, are so chosen that they produce a saw-tooth current of practically the same frequency as the squarewave current.

The synchronism is complete, however, by connecting the grid 89 of tube 8| to one lof the plates of the tube 80.V 'Ihe frequency control of both. tubes is therefore obtained by single controls 88a,

88h, 88o and 81a, 81h and 81o. y

Tube 82 is another double triode which is used i in the event that high signal voltages are required.

Tube 82 acts as an ampliiier in connection with the saw-tooth and square-wave oscillators.

The amplitude controls 92 and Stare used to control the voltage of the deflecting currents put into the vertical andhorizontal defiecting plates respectively, of the cathode ray tube and the amplitude controls 94 and 95 are used to control the voltages appliedfto the grids of the mixing tube 85 (T in Fig. 5). The mixed current obtained from the plates of this tube is applied to the frequency controlling tube F.

The same results, as obtained by purely electronicmeans, can very well be obtained by either purely mechanical or combined electronic and mechanical means. The mechanically frequency modulated oscillator is quite practical and readily made. A rapidly rotating motor driven condenser produces the frequency shift required. One precaution, however, must be taken in avoiding frictional contacts in the tuned circuit, which are invariably noisy, mostly on high frequencies. .The best method to avoid this is by usingfloa'ting rotors, which are n ot connected to the circuit, exl.

cept through their varying capacity to two opposite stators. Another precaution which must be taken is to properly balance the rotors dynamically, so as to avoid vibration. This can be obtained by using rotors having several blades, two, three or more. l v

The effect of such multi-bladed rotors is to speed up the number of images for a given motor speed. In ultra-high frequency work, where the periodical variation of capacity required is quite small and amounting only to a few micro-microfarads, I prefer to obtain the capacity variations' necessary by simply rotating a dielectric of high constant between two stator plates connected in the tuned circuit; Several such dielectric rotors can be coupled on one shaft to tune asmany circuits as required. `One of these rotors can be used for mechanically producing a source of sweep voltage, by the periodical charge and dlscharge of a condenser, as described in my copending applications, supra. Fig. 8 is an example of such a construction, in which 86a, 86h represent the two blades of a dielectric rotor having va 90 opening and rotating between one or Vtwo pairs of stator blades 91a, 91h and 98a, 98h. We have in fact two distinct. variable condensersl which can b e used in two different circuits or can be connected together for obtaining a larger variable capacitor.

The center of this rotorA has a metal bushing j 09 which is grounded throughthe shaft |05 of the motor |05 (Fig. 9) rotating it, and also two small metal sectors |00a, |00b, connecting each on the other side.

ly at a certain voltage or at ground potential, as

of the blades a and 88h.' A brush |0| is riding alternately either over the dielectric or over the grounded metal sectors insuch a way as to pass` from metal to dielectric exactly at the moment of maximum or minimum capacity of the condenser. This brush periodically discharges con" denser -|02 to ground which condenser becomes charged through a resistor |03 when the brush rides over the dielectric.

The condenser |02 .becomes amechanical source of sweep voltage whichisnoiselessbecause z the oniy frictional contact which takes placeis to either the dielectric or to a grounded part of the receiver, which is not apartof thetuned cir- The electrical nized dielectric condenser andsweepvoltage gen-j erator are shown in Fig `,9 infwhich, for the sake of simplicity, I show only oneperiodically tunedl circuit, an oscillator whichcan be the element B The synchronized conof the block diagrams.

denser andvsweep generator replace the' elements F and Gof those diagrams.

By a slight addition to this construction, I can d obtain an alternating coverage of two bands shown on two different lines on the screen of the thgde ray tube, as shown in block diagram On the same shaft |05 of this rotor, I mount a commutator composed'of two equal sectors |01 and |08, Fig. 10, of double the opening of the blades ssa, 96h, that is 180. oneof these sec'- tors isgof metal and grounded to the shaft, and thence tothe chassis; the other sector is of an insulating material. to a high resistance potentiometer ||0| connected on one side to a source of direct current (anode supply for example) and grounded This brush will be alternatethe commutator rotates; a square wave is consequently created, mechanically, which can serve through condenser I2 (for shifting the image on the cathode ray tube as explained before. The same commutator can serve for alternatingly selecting one of two condensers which tune the oscillator circuit; 'it can also serve for mechanically shutting off or reducing the power of an altitude-indicating oscillator, as described above.

s Such a mechanical commutator can be made to open the cathode circuit of the oscillator for predetermined periods of time corresponding to the angle of the commutator sectors. The transmitter vcan be keyed oi, for example, alternately during each part of that rotation cycle which produces images of signals on the screen of the receiver.

This can-be better seen in Fig. 11 where, instead of having acondenser permanently connected in the tuning` circuit, I show two condensers and ||3,e'ach being alternately con'- connectionsjofsuch a synchro-l A brush |09 is connected nected through brushes shown respectively at H4 and |09. to the ground. l

Two dierent frequency portions are then covered by the rotating condenser 96-91 previously described. By individually tuning thecondensers and H8, each -band may be separately shifted. Condenser can, as shown in Fig. 11, be controlled by a pressure controlled device such as an altimeter and condenser ||3 may be manually controlled for specialA purposes, as shown hereinafter. Y

'Ihe block diagram of Fig. 5 can be fully adapted to this arrangement.

The type of mechanically produced sweep volt' age just described has one disadvantage: Onehalf of the images are lost by grounding the condenser |02 half of the time. The result of this is more tendency` to flicker andless brilliancy of the image, as evident from Fig. 12. I can, however, advantageously,. combine electronic sweep and mechanically produced square wave with elimination of this disadvantage.

Figs. 13 andv 29 show such arrangements. In Fig. 13 the condenser |02 has been replaced by a saw-,tooth oscillator I6 whose grid 89 is syn,- chronized to a mechanical square-wave generator similar to the one heretofore described, but using the 90 sectors |01a, |08a, |011), |08b.

This form of sector alternately switches condensers and H3, at double the rate obtained before. The number of images obtained pn the screen is double, because veach alternate sawtooth' cycle serves to put on the screen one of Y the frequency bands covered.

In Fig. 29, I show a combination of electronic means and mechanical means which permit the use of double the number of images, with consequent double brightness of the signals. I nstead of using a motor which rotates a condenser, I use in this case aloud speaker unit ltiGA which replaces the motor |06 and has a fleld coil |15 and a moving coil .|80 which bears a metal disc 91d, whose distance from a,- similar disc `91e can vary at a rate which is determined by the vibration of said moving coil.

These discs Vare in fact the armatures of a periodically variable'condenser of a panoramic receiver, such as shown as 96-91 in Fig. 9. The `rate of frequency variation of this condenser is determined by the rate of vibration of this moving coil |80 which rate is determined by an aloscillator whose frequency is controlled by the local atmospheric pressure. I shall show now how Ican supplement this information with that f of a direction, which may be readily interpreted to indicate a given course, or to directly indicate "righ and left with respect to said course. Two transmitters have to b e used instead of one, each operating on a frequency slightly different from the other, each of these transmitters emitting a directional signal in such an angular relation to each other, as to create an equi-signal path along said` course.

Fig. 14 shows such an arrangement in. which T1 and T2 are such transmitters, each feeding respectively into the dipoles A1 and A2 at right angles, whereby the courses X1, X2 and Y1, Y2 are created. Supposing now that a panoramic receiver is covering a frequency band of 2.5 mc., for example, from,122.5 to 125 mc., spread over 2.5 inches of a cathode ray tube screen. Oneeighth inch separation between two signals would mean 0.125 mc. If the two signals produced by T1 and T2 are, in other words, 0.125 mc. apart from each other, they will appear on the screen as two deflections at 1A, separation. If the observer is on the equi-signal path, the peaks of ternating current produced by the sweep voltage generator I6 and amplified by tube |11. A

This frequency can be adjusted at wi11 by variable adjustments 81 and 28. The extent of frequency variation is determined by the amplitude of vibration of said moving coil |80 and condenser plate 91d and this is adjusted by ing able to follow much greater speeds than a double blade motor driven condenser, and is free from frictional noises.

In Fig. 1, I have shown a simple transmitter-` the two signals will appear equally high. If he is on one side, orV the other, one peak or the other will predominate. The amplitude ratio of the two signals will indicate the lnumber of degrees off-course.

This is very useful when the pilot wishes to keep within a certain fixed angular direction with respect to such a beacon. He adjusts the amplitude of one signal so as to bring its peak at a given reference line and he can read from the height of the other signal the angle off-course" on a calibrated screen.

Fig. 15 shows such an arrangement of a screen. Naturally, this pre-supposes the use of a series of such beacons, each sending radiations' having similar patterns, in other words, the use of standardized and properly adjusted antenna structures.

I have found that it is essential to keep the difference of wavelengths between these signals as small as possible, so that the number of wavelengths traveled by each signal within 4-5 miles from the station-where the signals are generally more erratic and more subjected to the effects of refiectionfrom obstacles-should be substantially equal, or dilering only by one or two wavelengths.

This reduces to practically zero the number of points where false indications would be obtained if this differencewould be greater. This isa fundamental part of my invention distinguishing it from the usualtype of dual frequency radio ranges, where no special precautions are taken to maintain this wavelength separation within a minimum` value. The panoramic re ceiver can be made of suicient selectivity to distinguish between two carriers of any frequency separation, as there are no interfering side-bands such as would be produced by modulating such carriers.

Two signals of very close frequency with their antenna elements quite close to each other are diilicult, however, to maintain properly tuned. There is a tendency for these two signals to pull" each other in synchronism or to create sde-bands by becoming intermodulated.

By proper shielding precautions it is possible` to run the two transmitters together.

I can avoid, however, completely these diiiculties, by sending signals intermittently through each antenna, in such a manner that when one on, the other is oil". This switching of the itennas, each operating on a predetermined lfferent, and adjacent, frequency can be obtained ther mechanically or electronically. The rst lethod has the advantage of great simplicity.

Fig. 16 shows such an arrangement vin which master oscillator IIS in the dotted rectangle as a frequency determined by inductance ined by either condenser ||8 alone or by conensers ||8 and ||9 in parallel. Condenser |9 lay be either set to a definite frequency or con- .'olled by a device These two condensers are eriodically connected in parallel by a rotary ommutator |2|l-|2|, turned by a motor |22. ne half, |20 of this commutator is constructed f metal and is grounded. The other half, |2| f the commutator is insulated. f Rapid commuation is obtained of two frequencies F1 and F2, he difference between these frequencies being .etermined by the capacitance of condenser IIS. ffultiplying or buiIer'- stages follow this masterscillator, and then a final amplier 23 is pro- 'ided. The output inductance |24 is connected o a commutator |25, and |21, in such amanier as to be alternately connected fat eachhalf `otation of this commutator with either antenna l1 or Az. Y

The position of all these commutator rings and segments is carefully arranged "so as to obtain in absolute synchronism between the frequency awitching and antenna switching. A common ;haft |28 is used to rotate all these commutator ings. This mechanical system has the common iisadvantage of requiring periodical mainteiance. For this reason, aswell as others, de- ;cribed hereinafter, I prefer an electronically :ontrolled dual-frequency, dual-directional system.

Fig. 17 shows in block diagram such a system. A master oscillator M periodically changes the frequency from Fi to F2, as controlled by a frequency determining circuit N which in turn is controlled by a periodic current, preferably a square-wave generator 0. The master oscillator may be coupled to multiplying or buffer stages P, or be fed directly into two final amplifiers T1 and T2. These amplifiers are permanently connected to their respective antennas A1 and A2 but only one operates at a time, as the keying tubes R1 and R2 alternatingly cut them oif or block their operation. These keying tubes are controlled by the same square-wave generator O which controls the frequency Fi or F2.

Fig. 18 shows the details of such a transmitter. The parts corresponding to the block diagram Fig. 17 are surrounded by dotted lines. rlIube |29 is a square-wave oscillator similar to tube 83 of Fig. 6. A push-pull amplier stage composed of tubes |30|3| follows it, the tube |3| acting as an amplifier phase inverting tube. Part of the square-wave voltage is applied through an amplitude controlling potentiometer |34 to the fre-v quency controlling tube |32 which `acts upon the oscillator tube ||6 just like the tube I5 acted upon the tube |4 in Fig. 4. 'I'he frequency variation is determined by the adjustment of potentiometer |34. The amplified push-pull squarewave impulses are applied to the keying tubes |33A and |3313 which respectively bias or block the final amplifying tubes |23A and |23B.

These tubesreceive their excitation from the master oscillator IIS, through the multiplying and buffer stages P, through a balanced grid line |35.v The two antennas A1 and A2 are permanently connected but operate alternatingly and only one-half of the total time.

As only one power amplifier draws plate and grid current at any one time, the requirements of the power supply are those of a single ended transmitter. Furthermore, as each power amplilfier has to dissipate current only during one-half of the time, the tubes used can be loaded up during the operation at much more than their ordinary continuous ratings, without harming them. The plate and grid meters |36A, |36B and |31A, |31B, are used for balancing the two ampliiers accurately.

Instead of using a master oscillatoi` which is electronically controlled, 'and followed by various stages and power amplifiers, it is quite practical to use two simple self-oscillating transmitters which work-continuously or are alternately keyed on and off, like the final amplifiers shown as |23A and |23B. This simplifies the construction very much. Such a double oscillator is represented in block diagram in Fig. 19 and can be visualized in detailsv from Fig. 18 in which the stages M, N and P, the grid line |35, and neutralizing condensers,

|38A and |38B are simply shunted. By using parallel line plate and grid circuits of very high Q, and by not heavily loading these oscillators, their frequency stability is quite good and they -make excellent simple direct right and "left indicating radio range beacons. In the block diagram Fig. 19, I have also omitted the keying tubes because the oscillator grids can easily be controlled directly by the square-wave generator O which applies sufficient voltage to entirely shut on each oscillator alternatingly. y

With reference to Fig. 18, this result would be obtained by connecting the two meters |31A and |31B, instead of to ground, to the cathode resistors |39 and |40 of the square-wave generator and replacing the tubes |33A and |33B by cathode biasing resistors.

In all these transmitter arrangements, the frequency can be either preset or can vary within certainlimits as controlled by a frequency controlling element such as an aneroid barometer, as shown inFig. 1. The two antennas, whose orlentation determines certain courses, can either be fixed or of variable orientation and canbe mounted either on a fixed body, or ori a mobile body. For example, such simple dual-transmitters of predetermined frequencies preset at a given small difference, can be located at predetermined intervals along a navigational air line to determine a given line of flight. Such a line may extend in a curve course. By spacing such transmitterssuiciently near each other and by properly setting each antenna, the flier can be guided along the given path. With a panoramic receiver aboard, the pilot can see when the aircraft passes through the intersection of two such equi-signal courses. x

Fig. 20 shows such a case where a series of such dual-frequency beacons Si, Sz and S3, are sol arranged as to lead a flier over a course Si, Pi-z, S2, Pz-a, Sa, in which-Pi-z and Pz-a represent the surfaces determined by the' intersections of the courses determined by S1 and Sz, and S2 and Ss, respectively. These intersections may be landing fields or other important points and it is important for some purposes to limit it to the smallest possible surface. It can be shown that the area P of such a surface is a function of the two distances Si-P and Sz-P of the angle w between the two courses and the angular opening a of each course. That is to samthe angular aeiaaos of the dial on the left corresponding to distance zero, indicating Chicago, will correspond to `lima.

on the screen. The dual frequency beacons will aircraft is olf-course. The use of the threshold control on the panoramic receiver, as explained hereinbefore, now becomes very important as it emphasizes small diierences of amplitude between signals. Square-law detectors may also be. used, instead of linear-detectors, for emphasizing such diierences.

Such an airline may use a series of such dualfrequency beacons whose average frequency (average between the two frequencies used) varies proportionatelly to the variation of distance of their location with respect to a fixed reference. This reference can be a line (a given meridian or parallel), or a point. In other words, let us say that the frequency band Fam. to Fmm. is used to cover a distance of D miles extending luetween two such iixed references. Each dual transmitter uses two frequencies fx and f's deterlfurther v which can be used along the distance D, and not to crowd them too much on the screen of a cathode ray tube of relatively small diameter, I prefer to combine some manual tuning with panoramic tuning and, at the same time, use an indicator showing what part of the band is tuned in, this indicator being calibrated in units of distance.

Such an arrangement is shown in Fig. 2l in which isi is the screen of a cathode ray tube and i632 is a slider which can move to right or left within certain limits by the action of idler pulleys |43, |04 and manually controlled pulley M5, over whicha steel string IIB is wound. This string is connected to the two ends of the slider 02.

'I'his slider can move so that either end of it can come in line with one extremity of the screen of the cathode ray tube. It is calibrated in.

miles, and their separation corresponds to the separtion between signals appearing on the cathode ray tube screen; for example, as shown in Fig. 21, when allv the way to the rightl it will. show the stations from the reference point (zero miles) up to 200 miles and when all the way to the left it will show the stations from 200 miles up to 400 miles. 'I'his is obtained by connecting the same pulley M5 with the shaft |57 of a rotor appear one after the other, further to the right, as the flier `progresses along the course, several being seen according to the height or distance of the iiier. The observer can. if he wishes to, gradually bring them to the center and maintain the true relationship between the readings on the card ISS, mileage indication on slider M2 and position of the signalen screen IGI. Such an arrangement as shown is the equivalent of multiplying the diameter of the screen by two, and, naturally this can be multiplied still more if desired. As the iiier reaches the end of the course marked on the card, he enters a new zone where the frequencies Fam-Frau. are repeated and he replaces the card |58 with a new one. resetting his dial to zero miles. Such a receiver, by reducing the sweep voltage applied through potentiometer 26 to the reactance tube, becomes an ordinary receiver tuned at the center frequncy defined hereinabove. The auditive device 3d will then reproduce the audible signals of any station corresponding to that center frequency and which can be marked as a hairline on the center of the oscillograph screen (Fig. 21)

'I'his dial arrangement can very well be used with a two-band panoramic receiver such as shown in Figs. 5, 6. '7, l1, 13, in which one band is controlled by one manual setting such as just described (condenser H3), and the other band by an automatic setting (condenser Il) determined, for example, by an altimetei".

In Fig. 21, I show such a combination dial. Above the screen Uil, a scale H of the diameter of the screen shows 0 in its center and is calibrated in altitudes up to 2000 feet above to the right and 2000 i'eet below to theleit of the center line. An altimeter dial H59 gives theactual altitudewhich in Fig. 2l is 5200 feet.

A signal E50 appears on the screen, above the line of beacon signals,- indicating the preesnce of a warning station'about 1000 feet above the observer, in other words, at 6200 feet. This may be a mountain peak or another plane, and this matter is easily determined, as it will be explained hereinafter, according to the rate offblinking" or interruption of the signal.

In the first case, the pilot knows that he must rise until the signal passes to the left of the center line, that is, below him.

In the second case,lcertain traftlc regulations are applied and as each pilot eithergoes higher or lower, theirvrespective change of position is seen` bythe two observers in their receivers.

The identiilcation of stations can be obtained .in various manners with a panoramic receiver,

vided the necessaryv controls for this purpose (see 8447, Fig. 4).

ceiver, continuously adjustable speed devices In a mechanically controlled re- 

